The present invention relates to a contact sensor for workpiece calipering having one spring parallelogram for each coordinate axis used for the measurement of translation.
Sensing heads for mechanical scanning of workpiece bodies in three-dimensional measuring instruments are known. Such sensors are either supported rotationally in two axes and translationally in the third, or translationally in all three. Translational execution is implemented by correspondingly arranged spring parallelograms.
Sensors also are known, wherein the measurement forces are applied by additional steps. In this manner the sensing position for read-out is the same in every case. Therefore, converting or correcting the measured data no longer is necessary.
Such sensors suffer from the drawback of relatively high costs required especially by multi-dimensional scanning to obtain the measurement forces.
In another design, the measurement force is not applied in special manner to the sensor. Rather, it is obtained from a sensor deflection of known magnitude, which then is combined by suitable measurement techniques with the value from the measurement detection system to provide the proper result. As regards a special case of such a design, a sensor deflection is less than the accuracy of the measuring instrument, so that this combination may be omitted.
The following problem is encountered with sensors of the last-mentioned kind; the deflection of the feeler point for the measurement under consideration should be as small as possible on technical grounds. This requires a relative steep slope of the force-distance relationship (stiff spring) for each degree of freedom of the feeler point in order to generate a given measuring force. On the other hand, a certain play in motion is required with respect to the sensor so that the sensing head may itself assume control of motion in the case of collisions between workpiece and sensor, and so it may immediately brake the motion in order to prevent destruction. However, a stiff spring and appreciable play in motion are contrary requirements.